The present invention relates to a radiation sensitive composition for forming an insulating film, an insulating film and a display device. More specifically, it relates to a negative type radiation sensitive composition suitable for the formation of an insulating film using radiation such as ultraviolet rays, deep ultraviolet rays, X-radiation, electron beam, molecular beam, xcex3-ray, synchrotron radiation or proton beam, an insulating film for a display device formed therefrom, and a display device having the insulating film.
An organic EL display device has small dependence on view angle as it emits light by itself and has various advantages such as excellent impact resistance, low voltage drive, low power consumption and high operation stability at a low temperature range as it is a solid device, in comparison with a liquid crystal display device. Since it is highly expected that the organic EL display device will be used particularly for mobile applications such as portable terminals and automobiles due to the above advantages, studies on the organic EL display device are under way energetically.
The production of such an organic EL display device is generally carried out by the following method. A transparent electrode (hole injection electrode) pattern such as a tin-doped indium oxide (ITO) pattern and a hole transport layer pattern are formed on a substrate. Then, an insulating film pattern and a cathode rib pattern are formed, followed by the patterning of an organic EL layer, an electron transport layer and a cathode by deposition in the case of a passive type organic EL display device. In the case of an active type organic EL display device, after an ITO pattern and an insulating film pattern which will become organic EL layer ribs are formed, an organic EL layer pattern is formed by a masking method or ink jet method, followed by the formation of an electron transport layer and a cathode (electron injection electrode).
In general, the organic EL layer is made from a base material such as Alq3 or BeBq3 doped with quinacridone or coumarine and the cathode is mainly made from a material essentially composed of a metal having a low work function such as Mg or Ag.
To meet recent demand for high resolution, an organic EL display device having a larger numerical aperture is now under study.
However, there is definite limitation to the improvement of the numerical aperture for the following reasons.
That is, to improve the numerical aperture of a passive type organic EL display device, the pattern widths of an insulating film and a cathode rib pattern need to be reduced. This requires a certain degree of strength and there is limitation to the reduction of pattern width from the viewpoint of resolution. Accordingly, a sufficiently large numerical aperture could not be obtained.
In an active type organic EL display device, to prevent a short circuit in an ITO pattern for each pixel, a certain space must be formed between pixels, thereby limiting the numerical aperture.
An active type organic EL display device having a structure capable of obtaining a larger numerical aperture is now under study.
This active type organic EL display device is produced by the following method, for example.
A drive terminal is formed on a glass substrate or the like, a first insulating film is formed as a flattening film on the terminal, and then a transparent electrode (hole injection electrode) pattern such as an ITO pattern is formed on the first insulating film. The formation of these patterns is generally carried out by a wet etching method.
A hole transport layer pattern is further formed on the transparent electrode pattern by a masking method. Thereafter, an ITO pattern, a second insulating film pattern which will become ribs for an organic EL layer and an organic EL layer pattern are formed by a masking method or ink jet method, followed by the formation of an electron transport layer and a cathode (electron injection electrode).
At this point, a 1 to 15 xcexcm long through hole or U-shaped depression must be formed in the first insulating film to make the ITO electrode (hole injection electrode) and the drive terminal conductive with each other.
It is known that an organic EL light emissive layer deteriorates quickly and its light emission is impeded when it contacts water even if it is a low-molecular weight light emitting layer or polymer light emitting layer. It is considered that water comes from environment or a trace amount of water adsorbed to an insulating film material permeates an organic EL layer little by little.
Heretofore, there has not been proposed a material capable of forming an insulating film which has resolution high enough to form a through hole or U-shaped depression for realizing a larger numerical aperture, excellent flattening capability and high resistance to a resist remover used for the formation of a transparent electrode and further prevents the permeation of impurities (mainly water) which impede light emission.
A thin film transistor (to be abbreviated as TFT hereinafter) liquid crystal display device is generally produced by opposing a TFT array substrate having TFT""s, electrode lines and capacitors formed on a glass substrate to a color filter substrate having a color filter formed on another glass substrate, joining them together using a sealer, injecting liquid crystals into the space between the substrates and sealing up the injection port with a sealer.
The above TFT array substrate is generally produced as follows. TFT elements, display electrodes, scanning lines (gate electrodes), signal lines (drain electrodes) and capacitors are first formed on a glass substrate. Thereafter, an interlayer insulating film is formed on these, a contact hole pattern for interconnecting pixel electrodes and source electrodes is formed, and then transparent pixel electrodes (ITO) are formed on the interlayer insulating film. Thereafter, the transparent pixel electrodes are partitioned for each pixel by etching, and a liquid crystal alignment film is formed and rubbed.
When an end portion of each pixel electrode is placed upon an end portion of a scanning line or signal line to increase the numerical aperture as much as possible, the above interlayer insulating film is formed to insulate them from each other. A radiation sensitive composition from which an interlayer insulating film having a desired pattern shape and excellent flatting capability is obtained from a small number of steps is widely used as a material for the above interlayer insulating film. JP-A 7-98502, JP-A 7-98503 and JP-A 7-140648 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d) disclose a combination of a novolak resin or phenolic resin such as polyhydroxystyrene and a quinonediazide-based sensitizer, and Japanese Patent No. 3003064, JP-A 10-153854, JP-A 2001-281853 and JP-A 2001-281861 disclose a combination of an acrylic resin and a quinonediazide-based sensitizer as the materials.
As described above, after such an interlayer insulating film is formed on a substrate, the step of forming a transparent pixel electrode and a liquid crystal alignment film is carried out, and the interlayer insulating film is heated at a high temperature in the above step. Since conventionally known materials for forming an interlayer insulating film are unsatisfactory in terms of heat resistance, they become yellow or brown in the above step with the result of greatly reduced transparency. To avoid this phenomenon, the temperature for heating the transparent electrode film must be set to a certain temperature or lower. If so, the formed transparent electrode film hardly obtains desired electric properties, particularly sufficiently low electric resistance.
After the interlayer insulating film is formed on the substrate, it is supplied to the step of forming an electrode and exposed to organic solvents such as an etchant for the patterning of the electrode and a resist remover. Therefore, the interlayer insulating film needs high solvent resistance so that it is not swollen, deformed or peeled of f from the substrate by these solvents. Further, higher radiation sensitivity and more excellent developability are required from the viewpoint of production yield.
However, there has been unknown a radiation sensitive composition suitable for the formation of an interlayer insulating film for a liquid crystal display device, which has high radiation sensitivity, excellent developability, high heat resistance, high transparency and excellent solvent resistance.
It is therefore an object of the present invention to provide a radiation sensitive composition for forming an insulating film for an organic EL display device, which has resolution high enough to form a through hole or U-shaped depression, excellent flattening capability and high resistance to a resist remover used to form a transparent electrode, and prevents the permeation of impurities (mainly water) which impede light emission.
It is another object of the present invention to provide a radiation sensitive composition which has high radiation sensitivity, excellent developability, high heat resistance, high transparency and excellent solvent resistance and is suitable for the formation of an interlayer insulating film for a liquid crystal display device.
It is still another object of the present invention to provide an insulating film for an organic EL display device or liquid crystal display device formed from the above composition.
It is a further object of the present invention to provide an organic EL display device or liquid crystal display device having the above insulating film.
Other objects and advantages of the present invention will become apparent from the following description.
According to the present invention, firstly, the above objects and advantages of the present invention are attained by a radiation sensitive composition which comprises:
(A1) at least one compound selected from the group consisting of a silane compound represented by the following formula (1):
(R1)pSi(X)4-pxe2x80x83xe2x80x83(1)
wherein R1 is an unhydrolyzable organic group having 1 to 12 carbon atoms, X is a hydrolyzable group, and p is an integer of 0 to 3,
a hydrolyzate thereof and a condensate of the hydrolyzate; and (A2) a compound which generates an acid or base upon exposure to radiation, and
(B) which is used to form an insulating film for an organic EL display device.
According to the present invention, secondly, the above objects and advantages of the present invention are attained by a radiation sensitive composition which comprises (A1) at least one compound selected from the group consisting of a silane compound represented by the above formula (1), a hydrolyzate thereof and a condensate of the hydrolyzate, and (A2) a compound which generates an acid or base upon exposure to radiation, and (B) which is used to form an interlayer insulating film for a liquid crystal display device.
According to the present invention, thirdly, the above objects and advantages of the present invention are attained by an insulating film for an organic EL display device or a liquid crystal display device, which is formed from the above radiation sensitive composition of the present invention.
According to the present invention, in the fourth place, the above objects and advantages of the present invention are attained by an organic EL display device or liquid crystal display device having the above insulating film.